Tomato yellow leaf curl virus meets match

One of the world’s most damaging tomato diseases may have met its match now that University of Florida researchers have found a way to give plants resistance to tomato yellow leaf curl virus.

A team of researchers at UF’s Institute of Food and Agricultural Sciences have created a genetically engineered tomato plant that can shut down the virus, a pathogen that has spread rapidly around the globe, devastating tomato crops and forcing growers to increase their use of expensive and environmentally harmful pesticides.

“If this virus appears in your field, you can easily lose your entire crop,” said Jane Polston, a plant virologist with UF’s Institute of Food and Agricultural Sciences. “And even the growers who don’t get the virus are spending lots of money on pesticides to stop the insect that carries the virus.”

Though it is difficult to assign a dollar figure to damage caused by the virus, yellow leaf curl is recognized as the most important limiting factor in many countries, Polston said. Widely found throughout the Mediterranean region, the disease spread to the Western Hemisphere in the early 1990s, wiping out the entire tomato industry in the Dominican Republic.

Polston was the first scientist to identify the virus in a Florida tomato field. That 1997 discovery created a stir among growers, who recognized the virus as a major threat to the nation’s tomato crop, which nets farmers more than $1 billion each year according to the U.S. Department of Agriculture. The disease is not likely to affect consumer prices for tomatoes in the near future, due to high levels of production in Mexico and other countries still free of the virus.

Once infected with the virus, a tomato plant stops growing normally and no longer produces marketable fruit, meaning that an outbreak early in the season can wipe out an entire season’ crop. The whitefly, an insect commonly found in tomato-growing areas, can pass the virus from plant to plant with only minimal contact.

U.S. farmers have been able to limit the disease’s damage, but only by boosting the use of pesticides that kill the whitefly. It’s an expensive solution, and less than ideal for an industry looking to reduce its use of chemicals to control pests. And it hasn’t stopped the spread of the disease, which has been found in fields from Louisiana to North Carolina.

Even as they announced that the virus had arrived in Florida, UF researchers had an inkling of how to stop it. Using a technique they’d employed against a distantly related tomato virus, Polston and UF plant pathologist Ernest Hiebert snipped a piece off the gene that regulates replication in the tomato yellow leaf curl virus and spliced that genetic information into tomato plants. Their hope was that the transferred gene would give the tomato’s immune system the ability to recognize the virus and shut it down before it damages the plant.

The plan worked. As the researchers reported in the May issue of the journal Phytopathology, plants with the transferred genetic information grow normally and produce healthy fruit even after they’re exposed to the virus.

Other institutions have produced tomato plants that resist tomato yellow leaf curl disease, the researchers say. But those plants, created by crossing existing tomato varieties with close relatives of the tomato, produce fruit that is smaller and generally lower in quality than non-resistant varieties.

“The disease-resistant cultivars that are currently in use are good for some growers, but they’re not for everyone,” Hiebert said. “In Florida, many people are growing tomatoes for the restaurant market, and restaurants want big tomatoes — the kind you slice and put on a hamburger.”

The researchers spliced the gene into a tomato breeding line that was developed at UF and has not yet been released to the public, but they say the gene-splicing technique can likely be used to grant virus resistance to any tomato variety without changing the size or quality of its fruit.

The researchers are currently seeking corporate partners to use their technology in commercially available tomato varieties, but it could still be years before the new virus-resistant tomatoes hit grocery store shelves.

Commercial availability of a virus-resistant tomato can’t come too soon for growers such as D.C. McClure, vice-president of West Coast Tomato in Palmetto, Fla. Like many growers, West Coast Tomato has waged costly battles with the virus ever since it appeared in the area.

“We’ve pulled up and replanted entire fields of tomatoes this year to stop the virus from spreading, and I’m sure we’re not alone in doing that,” McClure said. “Everybody is dealing with this, and the only question at this point is whether the virus will appear early in the season or late in the season.”

McClure said his company has already experimented with earlier disease-resistant varieties, and found them lacking.

“Whether it’s fruit size or productivity of the plant, there always seems to be something missing,” he said. “If you can produce a tomato plant that resists this virus and still has all the qualities of the varieties we’re growing now, I guarantee growers will want it.”